Copper-nickel-silicon alloys

ABSTRACT

A copper base alloy having an improved combination of yield strength and electrical conductivity consisting essentially of between about 1.0 and about 6.0 weight percent Ni, up to about 3.0 weight percent Co, between about 0.5 and about 2.0 weight percent Si, between about 0.01 and about 0.5 weight percent Mg, up to about 1.0 weight percent Cr, up to about 1.0 weight percent Sn, and up to about 1.0 weight percent Mn, the balance being copper and impurities, the alloy processed to have a yield strength of at least about 137 ksi, and an electrical conductivity of at least about 25% IACS.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 61/044,900, filed Apr. 14, 2008, and U.S.Provisional Patent Application No. 61/016,441, filed Dec. 21, 2007, theentire disclosures of which are incorporated herein, by reference.

BACKGROUND

This invention relates to copper base alloys, and in particular tocopper-nickel-silicon base alloys.

Copper-nickel-silicon base alloys are widely used for the production ofhigh strength, electrically conductive parts such as connectors and leadframes. C7025, developed by Olin Corporation, is an important example ofa copper-nickel-silicon base alloy that provides good mechanical (yieldstrength 95 ksi -110 ksi) and good electrical properties (35% IACS) .See U.S. Pat. Nos. 4,594,221 and 4,728,372, incorporated herein byreference. More recently, C7035, a cobalt modified copper, nickel,silicon alloy, has been developed by Olin Corporation and Wieland Werke,which can provide even better mechanical (yield strength 100 ksi -130ksi) and electrical properties (40-55% IACS). See U.S. Pat. No.7,182,823, incorporated herein by reference.

The properties of copper alloys that can be important includeformability, conductivity, strength, ductility, and resistance to stressrelaxation.

Formability is typically evaluated by a bend test where copper stripsare bent 90° around a mandrel of known radius. A roller bend testemploys a roller to form the strip around the mandrel. Alternatively, av-block test uses the mandrel to push the strip into an open die,forcing it to conform to the radius of the mandrel. For both tests theminimum bend radius (mbr) as a function of strip thickness (t) is thenreported as mbr/t. The minimum bend radius is the smallest radiusmandrel around which a strip can be bent without cracks visible at amagnification of 10× to 20×. Generally mbr/t is reported for both goodway bends, defined as the bend axis is normal to the rolling direction,and for bad way bends, defined as the bend axis is parallel to therolling direction. An mbr/t of up to 4 t for both good way bends and badway bends is deemed to constitute good formability. More preferred is anmbr/t of up to 2.

Electrical conductivity is typically measured as a percentage of IACS.IACS refers to International Annealed Copper Standard that assigns“pure” copper a conductivity value of 100% IACS at 20° C. Throughoutthis disclosure, all electrical and mechanical testing is performed atroom temperature, nominally 20° C., unless otherwise specified. Thequalifying expression “about” indicates that exactitude is not requiredand should be interpreted as +/−10% of a recited value.

Strength is usually measured as yield strength. A high strength copperalloy has a yield strength in excess of 95 ksi (655.1 MPa) andpreferably in excess of 110 ksi (758.5 MPa). As the gauge of the copperalloy formed into components decreases and as miniaturization of thesecomponents continues, a combination of strength and conductivity for agiven temper will be more important than either strength or conductivityviewed alone.

Ductility can be measured by elongation. One measure of elongation isA10 elongation, which is the permanent extension of the gauge lengthafter fracture, expressed as a percentage of the original gauge lengthL₀ where L₀ is taken equal to 10 mm.

Acceptable resistance to stress relaxation is viewed as at least 70% ofan imparted stress remaining after a test sample is exposed to atemperature of 150° C. for 3000 hours and at least 90% of an impartedstress remaining after a test sample is exposed to a temperature of 105°C. for 1000 hours.

Stress relaxation resistance was measured via the ring method [Fox A.:Research and Standards 4 (1964) 480] wherein a strip of 50 mm length isclamped onto the outer radius of a steel ring initiating stress at theouter surface of the strip. With exposure to elevated temperatureselastic stresses change into plastic deformation. This process dependsupon time, temperature and initial stress defined by the radius of thesteel ring. Experiments were performed between 50° C./96 h and 210°C./384 h. After each annealing the remaining flexion of the strip ismeasured and the corresponding stress reduction calculated according to[Graves G. B.: Wire Industry 46 (1979) 421]. Using theLarson-Miller-Parameter P an extrapolation from the performed short timeexperiments at higher temperatures to long time experiments at lowertemperatures can be done [Boegel A.: Metall 48 (1994) 872].

Stress relaxation may also be measured by a lift-off method as describedin ASTM (American Society for Testing and Materials) Standard E328-86.This test measures the reduction in stress in a copper alloy sample heldat fixed strain for times up to 3000 hours. The technique consists ofconstraining the free end of a cantilever beam to a fixed deflection andmeasuring the load exerted by the beam on the constraint as a functionof time at temperature. This is accomplished by securing the cantileverbeam test sample in a specially designed test rack. The standard testcondition is to load the cantilever beam to 80% of the room temperature0.2% offset yield strength. If the calculated deflection exceeds about0.2 inch, the initial stress is reduced until the deflection is lessthan 0.2 inch and the load is recalculated. The test procedure is toload the cantilever beam to the calculated load value, adjust a threadedscrew in the test rack to maintain the deflection, and locking thethreaded screw in place with a nut. The load required to lift thecantilever beam from the threaded screw is the initial load. The testrack is placed in a furnace set to a desired test temperature. The testrack is periodically removed, allowed to cool to room temperature, andthe load required to lift the cantilever beam from the threaded screw ismeasured. The percent stress remaining at the selected log times iscalculated and the data are plotted on semi-log graph paper with stressremaining on the ordinate (vertical) and log time on the abscissa(horizontal). A straight line is fitted through the data using a linearregression technique. Interpolation and extrapolation are used toproduce stress remaining values at 1, 1000, 3000, and 100,000 hours.

The resistance to stress relaxation is orientation sensitive and may bereported in the longitudinal (L) direction where 0° testing is conductedwith the long dimension of the test sample in the direction of striprolling and the deflection of the test sample is parallel to the striprolling direction. The resistance to stress relaxation may be reportedin the transverse (T) direction where 90° testing is conducted with thelong dimension of the test sample perpendicular to the strip rollingdirection and the deflection of the test sample is perpendicular to thestrip rolling direction.

Table 1 shows the mechanical and electrical properties of some of thecommercially available copper alloys of which the inventors are aware:

TABLE 1 Examples of properties of currently available Be-free Cu-basedalloys EI. Conductivity Yield Alloy Company Composition (% IACS)Strength, ksi C7025 Olin Brass Cu + 3.0Ni + 0.60Si + 0.15Mg >35  95-110EFTEC-75 Furukawa Cu + 3.2Ni + 0.65Si + 0.5Zn + 0.50Sn 25 116  EFTEC-23ZFurukawa Cu + 2.5Ni + 0.6Si + 0.5Zn + 0.03Ag 53 101-116 EFTEC-97Furukawa Cu + 2.3Ni + 0.55Si + 0.5Zn + 0.15Sn + 0.1Mg 40 110  EFTEC-98Furukawa Unknown 38 104-136 EFTEC-98S Furukawa Cu + 3.8Ni + 0.93Si +0.48Zn + 0.18Sn + 0.13Mg + 0.3Cr 38  95-129 K62 Wieland Cu + 0.3Cr +0.4Ni + 0.6Sn + 0.03Ti 52 100  KLF-125 Kobe Steel Cu + 3.2Ni + 0.70Si +0.3Zn + 1.25Mn 35 100  CAC-65 Kobe Steel Cu + 3.2Ni + 0.70Si + 1.0Zn +0.50Sn 46 94 MAX 251 Mitsubishi Cu + 2.0Ni + 0.50Si + 0.50Sn 45 89Shindo Max375 Mitsubishi Cu + 2.85Ni + 0.7Si + 0.5Zn + 0.5Sn + 0.015Mg42  91-116 KLF-1 Kobe Steel Cu + 3.2Ni + 0.70Si + 0.3Zn + 0.05Mn 55 88C7027 Olin Brass Cu + 2.0Ni + 0.60Si + 0.60Fe + 0.50Sn >40 >80 C18080/K88 Olin/Wieland Cu + 0.5Cr + 0.1Ag + 0.08Fe + 0.06Ti + 0.03Si 8080 C18070/K75 Wieland Cu + 0.3Cr + 0.1Ti + 0.02Si >75 70 PMC 102Poongsan Cu + 1.3Ni + 0.25Si + 0.05P 60 75 C7035/K57 Olin/Wieland Cu +1.4Ni + 1.1Co + 0.6Si >45 110-130 NKC388 Nippon Mining Cu + 3.8Ni +0.85Si + 0.18Mg − 0.1Mn 35-45 112-125 HCL 305 Hitachi Cu + 2.5Ni +0.5Si + 1.7Zn + 0.02P 42  87-102 HCL 307 Hitachi Cu + 3.0Ni + 0.7Si +1.7Zn + 0.3Sn + 0.02P 35 102-112

As good as these alloys are, and as widespread their use, there remainapplications where alloys with higher strength and in particular higherstrength without sacrificing other desirable properties such asconductivity, resistance to stress relaxation, and/or formability. Whileberyllium coppers can provide high strength, because of their berylliumcontent, they are not suitable for many applications. Amongberyllium-free copper alloys, high strength (e.g., yield strength aboveabout 130 ksi) is usually accompanied by significant diminishment ofother desirable properties, in particular formability.

SUMMARY

One aspect of the present invention is an age-hardeningcopper-nickel-silicon base alloy that can be processed to make acommercially useful strip product for use in electrical connectors andinterconnections for the automotive and multimedia industries, inparticular, and for any other applications requiring high yield strengthand moderately high electrical conductivity in a strip, plate, wire orcasting. Another aspect of the present invention is a processing methodto make a commercially useful strip product for use in electricalconnectors and interconnections for the automotive and multimediaindustries and any other applications requiring high yield strength andmoderately high electrical conductivity.

In accordance with one preferred embodiment of this invention, acopper-nickel-silicon base alloy having an improved combination of yieldstrength and electrical conductivity is provided that consistsessentially of between about 1.0 and about 6.0 weight percent Ni, up toabout 3.0 weight percent Co, between about 0.5 and about 2.0 weightpercent Si, between about 0.01 and about 0.5 weight percent Mg, up toabout 1.0 weight percent Cr, up to about 1.0 weight percent Sn, and upto about 1.0 weight percent Mn, the balance being copper and impurities.This alloy is processed to have a yield strength of at least about 137ksi, and an electrical conductivity of at least about 32% IACS.

In accordance with another preferred embodiment of this invention, acopper base alloy having an improved combination of yield strength andelectrical conductivity is provided that consists essentially of:between about 3.0 and about 5.0 weight percent Ni; up to about 2.0weight percent Co; between about 0.7 and about 1.5 weight percent Si;between about 0.03 and about 0.25 weight percent Mg; up to about 0.6weight percent Cr; up to about 1.0 weight percent Sn, and up to about1.0 weight percent Mn, the balance being copper and impurities. Thisalloy is processed to have a yield strength of at least about 137 ksi,and an electrical conductivity of at least about 32% IACS.

In accordance with another preferred embodiment of this invention, acopper-nickel-silicon base alloy having an improved combination of yieldstrength and electrical conductivity is provided that consistsessentially of: between about 3.5 and about 3.9 weight percent Ni;between about 0.8 and about 1.0 weight percent Co; between about 1.0 andabout 1.2 weight percent Si; between about 0.05 and about 0.15 weightpercent Mg; up to about 0.1 weight percent Cr; up to about 1.0 weightpercent Sn, and up to about 1.0 weight percent Mn, the balance beingcopper and impurities. This alloy is processed to have a yield strengthof at least about 137 ksi, and an electrical conductivity of at leastabout 32% IACS.

The alloys are preferably processed to have a yield strength of at leastabout 137 ksi, and an electrical conductivity of at least about 38%IACS, more preferably to have a yield strength of at least about 143ksi, and an electrical conductivity of at least about 37% IACS, and mostpreferably to have a yield strength of at least about 157 ksi, and anelectrical conductivity of at least about 32% IACS.

The ratio of (Ni+Co)/(Si−Cr/5) is preferably between about 3 and about7, and more preferably between about 3.5 and about 5.0. The Ratio ofNi/Co is preferably between about 3 and about 5.

The alloys and processing methods of the various embodiments providecopper base alloys having an improved combination of yield strength andelectrical conductivity, and preferably stress relaxation resistance aswell. In particular the alloys have higher strength and greaterresistance to stress relaxation than previously achieved with Cu—Ni—Sialloys, while maintaining reasonable levels of conductivity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart of the treatment of the alloys in Example 1;

FIG. 2 is a flow chart of the treatment of the alloys in Example 2;

FIG. 3 is a flow chart of the treatment of the alloys in Example 3;

FIG. 4 is a graph of the yield strength versus conductivity for thealloys of Example 3;

FIG. 5 is a graph of yield strength versus bend formability (MBR/t) forthe alloys of Example 3;

FIG. 6 is a flow chart of the treatment of the alloys of Example 4;

FIG. 7 is a graph of yield strength versus conductivity for the alloysof Table 5 processed by a SA-CR-age-CR-age process of Example 4;

FIG. 8 is a graph of yield strength versus bend formability (MBR/t) forthe alloys of Table 5 processed by SA-CR-age-CR-age process of Example4;

FIG. 9 is flow chart of the treatment of the alloys in Example 5;

FIG. 10 is a graph of yield strength vs Ni/Co ratio for alloys withoutchromium having similar alloying levels of Example 5;

FIG. 11 is flow chart of the treatment of the alloys in Example 6;

FIG. 12 is a flow chart of the treatment of the alloys in Example 7;

FIG. 13 is a graph showing the effect of stoichiometric ratio on yieldstrength in copper-nickel-chromium-silicon alloys from Example 7;

FIG. 14 is a graph showing the effect of stoichiometric ratio on yieldstrength in copper-nickel-cobalt-silicon alloys from Example 7;

FIG. 15 is a graph showing the effect of effect of stoichiometric ratioon yield strength in copper-nickel-chromium-cobalt-silicon alloys fromExample 7;

FIG. 16 is a graph showing the effect of stoichiometric ratio onelectrical conductivity in copper-nickel-chromium-silicon alloys fromExample 7;

FIG. 17 is a graph showing the effect of stoichiometric ratio onelectrical conductivity in copper-nickel-cobalt-silicon alloys fromExample 7;

FIG. 18 is a graph showing the effect of stoichiometric ratio onelectrical conductivity in copper-nickel-chromium-cobalt-silicon alloysfrom Example 7;

FIG. 19 is a flow chart of the treatment of the alloys in Example 8;

FIG. 20 is a graph showing the effect of stoichiometric ratio on % IACSin Example 8 alloys processed by the SA-CR-age-CR-age approach with 475°C./300° C. ages.

FIG. 21 is a graph showing the effect of stoichiometric ratio on yieldstrength in Example 8 alloys processed by the SA-CR-age-CR-age approachwith 475° C./300° C. ages;

FIG. 22 is a flow chart of the treatment of the alloys in Example 9

FIG. 23 is a schematic diagram of tapered edge hot rolling specimen;

FIG. 24 is a photograph of hot rolled K224 (without Cr), showing largeedge cracks;

FIG. 25 is a photograph of hot rolled K225 (0.11 Cr), showing no edgecracks;

FIG. 26A is photograph of the results from tool wear testing of non-Cralloy RN033407; and

FIG. 26B is a photograph of the Result from tool wear test ofCr-containing alloy RN834062;

FIG. 27 is a flow chart of the treatment of the alloys in Example 10;

FIG. 28 is a graph showing the effect of stoichiometric ratio on % IACSin Example 8 and Example 10 (low Cr and Mn) alloys processed by theSA-CR-age-CR-age approach with 475° C./300° C. ages; and

FIG. 29 is a graph showing the effect of stoichiometric ratio on yieldstrength in Example 8 and Example 10 (low Cr and Mn) alloys processed bythe SA-CR-age-CR-age approach with 475° C./300° C. ages;

FIG. 30 is a flow chart of the treatment of the alloys in Example 11;and

FIG. 31 is a flow chart of the treatment of the alloys in Example 12;

FIG. 32 is a flow chart of the treatment of the alloys in Example 13;

FIG. 33 is a flow chart of the treatment of the alloys in Example 14;

FIG. 34 is a flow chart of the treatment of the alloys in Example 15;

FIG. 35 is a flow chart of the treatment of the alloys in Example 16;

FIG. 36 is a graph of 90° V-block-MBR/t BW versus yield strength foralloys and processes of Examples 13, 14, 15, and 16; and

FIG. 37 is a graph of % IACS versus yield strength for alloys andprocesses of Examples 13, 14, 15, and 16.

DETAILED DESCRIPTION

There is a need in the marketplace for copper strip alloys with higherstrength and electrical conductivity, along with good stress relaxationresistance. This combination of properties is particularly important forparts that are formed into various electrical interconnections for usein multimedia electrical connector and terminal applications.Commercially available copper alloys, such as C510 (phosphor bronze),C7025, C7035, C17410 and C17460 are being used in these applications fortheir generally favorable combinations of strength and conductivity.However, while these alloys have adequate strength for most currentcarrying applications, the continuing trend for miniaturization ofcomponents demands copper alloys that offer high strength in combinationwith reasonably good electrical conductivity and reasonably good stressrelaxation resistance along with reasonable cost. It is also desirableto minimize or eliminate potentially toxic alloying elements such asberyllium.

Alloys that are used for multimedia interconnects require high strengthto avoid damage during connector insertion and to maintain good contactforce while in service. For these applications, good but not especiallyhigh electrical conductivity is all that is required, since theconductivity merely needs to be enough to carry a signal current, andneed not be the high levels needed to avoid excessive I²R heating inhigher power applications. For these applications, there are even morestringent requirements for mechanical stability at room and slightlyelevated service temperatures, as characterized by good stressrelaxation resistance at about 100° C., for example.

The alloy compositions of the preferred embodiments of this invention,and the scheme used to process to the finish tempers surprisinglyprovide highly desirable combination of properties for meeting the needsof both automotive and multimedia applications, namely very highstrength along with moderately high conductivity. In particular, thealloys of the preferred embodiments of the present invention are capableof being processed to strip products with combinations of yieldstrength/electrical conductivity of at least about 137 ksi with aconductivity of at least about 38% IACS, more preferably a yieldstrength of at least about 143 ksi, with a conductivity of at leastabout 37% IACS, and most preferably a yield strength of about 157 ksi,with a conductivity of at least about 32% IACS.

The alloys of the preferred embodiment of the present invention, have animproved combination of yield strength and electrical conductivity, goodstress relaxation resistance, along with modest levels of bendability,consist essentially of from about 1.0 to about 6.0 weight percentnickel, from about 0.5 to about 2.0 weight percent silicon, from 0.0 toabout 3.0 weight percent cobalt, from about 0.01 to about 0.5 weightpercent magnesium, from 0.0 to about 1.0 weight percent chromium, andfrom 0.0 to about 1.0 weight percent of each of tin and manganese, thebalance of the alloy being copper and impurities. More preferably, thealloy consists essentially of from about 3.0 to about 5.0 weight percentnickel, from about 0.7 and about 1.5 weight percent silicon, from 0.0 toabout 2.0 weight percent cobalt, from about 0.03 to about 0.25 weightpercent magnesium, from about 0.0 to about 0.6% weight percent chromium,and from 0.0 to 1.0 weight percent of each of tin and manganese, thebalance being copper and impurities. Where an optimum level of yieldstrength and electrical conductivity is needed, e.g. a combination of140 ksi YS/30% IACS, the most preferred alloy ranges are from about 3.5to about 3.9 weight percent nickel; from about 1.0 to about 1.2 weightpercent silicon; from about 0.8 to about 1.0 weight percent cobalt, fromabout 0.05 to about 0.15 weight percent magnesium, from 0 to about 0.1weight percent chromium, and from 0.0 to about 1.0 weight percent ofeach of tin and manganese, the balance being copper and impurities.Generally, excessive coarse second phases are present when alloyingelements are substantially beyond the indicated upper limits.

The electrical conductivity and yield strength of the alloy are highestwhen the (Ni+Co)/(Si−Cr/S) ratio is controlled between about 3 and about7, and more preferably between about 3.5 and about 5. The ratio of Ni/Cois optimal for yield strength and conductivity when controlled betweenabout 3 and about 5.

Magnesium generally increases stress relaxation resistance and softeningresistance in the finished products; it also increases softeningresistance during in-process aging annealing heat treatments. Whenpresent at low levels, Sn generally provides solid solutionstrengthening and also increases softening resistance during in-processaging annealing heat treatments, without excessively harmingconductivity. Low levels of Mn generally improve bend formability,although with a loss of conductivity.

The preferred embodiment of the process of the present inventioncomprises melting and casting; hot rolling (preferably from 750° to1050° C.), optional milling to remove oxide, and an optionalhomogenization or intermediate bell anneal, cold rolling to a convenientgauge for solutionizing, solution annealing treatment (preferably at800°-1050° C. for 10 seconds to one hour) followed by a quench or rapidcool to ambient temperature to obtain an electrical conductivity of lessthan about 20% IACS (11.6 MS/m) and an equiaxed grain size of about 5-20μm; a 0 to 75% cold rolling reduction in thickness; an age hardeninganneal (preferably at 300-600° C. from 10 minutes to 10 hours); andoptionally a further cold rolling 10 to 75% reduction in thickness tofinish gauge; and second age hardening anneal (preferably at 250 to 500°C. for 10 minutes to 10 hours). The resulting alloy can also beprocessed to finish gauge without using an in-process solutionizing heattreatment by using cycles of lower temperature bell annealing treatmentswith intervening cold work. In addition, one or more optionalrecrystallization anneal(s) may be added to the process during thereduction from hot rolled gauge to the thickness appropriate forsolutionizing.

The preferred scheme to result in alloy with a yield strength of atleast about 140 ksi, and a conductivity of at least about 30% IACSconductivity involves solutionizing at about 900° to 1000° C., coldrolling by about 25%, aging at about 450°-500° C. for 3-9 hours, coldrolling by about 20-25% to finish gauge, and aging 300°-350° C. for 3-9hours.

While this disclosure is particularly drawn to a process for themanufacture of copper alloy strip, the alloys of the invention and theprocesses of the invention are equally amenable to the manufacture ofother copper alloy products, such as foil, wire, bar and tube. Inaddition, processes other than conventional casting, such as stripcasting, powder metallurgy and spray casting are also within the scopeof the invention.

The alloys and methods of the preferred embodiments will be betterunderstood from the following illustrative examples:

Example 1 Increasing Alloy Levels Increases Strength; CobaltSubstitution Improves Both Strength and Conductivity

A series of ten pound laboratory ingots with the compositions listed inTable 2 were melted in a silica crucible and Durville cast into steelmolds, which after gating were approximately 4″×4″×1.75″. FIG. 1 is aflow chart of the process of this Example 1. After soaking two hours at900° C. they were hot rolled in three passes to 1.1″ (1.6″/1.35″/1.1″),reheated at 900° C. for 10 minutes, and further hot rolled in threepasses to 0.50″ (0.9″/0.7″/0.5″), followed by a water quench, followedby a homogenization or over-aging anneal at 590° for 6 hours. Aftertrimming and milling to remove the surface oxide, the alloys were coldrolled to 0.012″ and solution heat treated in a fluidized bed furnacefor the time and temperature listed in Table 2. Time and temperaturewere selected to achieve approximately constant grain size. The alloyswere then subjected to an aging anneal of 400° to 500° C. for 3 hours,designed to increase strength and conductivity. The alloys were thencold rolled 25% to 0.009″ and aged at 300° to 400° C. for 4 hours.Properties measured after the second age anneal are presented in Table3. The data indicate that yield strength increases with increasingalloying levels in the ternary alloys J994 through J999, from 127 to 141ksi yield strength when Si levels range from 0.8 to 1.3%, respectively.Comparing J994, K001 and K002 to examine the effect of Co on alloys near0.8% Si, the substitution of Co for Ni increases both yield strength andconductivity. Considering a Co substitution for Ni in alloys with ˜1.2%Si, K003 shows a decrease in yield strength and an increase inconductivity, while K004 shows an increase in yield strength anddecrease in conductivity when compared to J998.

Having a Ni/Co ratio of about 3 (K002 and K004) leads to a higherstrength than a Ni/Co ratio of 1 (K001 and K003), particularly at thehigher Si level. Mn alloys K011 and K012 show evidence that Mnsubstitution for Ni improves the strength/bend properties, but at asignificant loss of conductivity. Sn appears to provide solid solutionstrengthening, when comparing J994 to K036 and K037.

TABLE 2 Alloys of Examples 1 and 2 Grain Solution Size, Alloy Analyzedcomposition, wt % Anneal conditions μm J994 Cu—3.33Ni—0.81Si  850° C. -1 minute 11.2 J995 Cu—3.78Ni—0.92Si  900° C. - 1 minute 16.5 J996Cu—4.17Ni—1.03Si  900° C. - 1 minute 22.1 J997 Cu—4.48Ni—1.12Si  900°C. - 1 minute 22.1 J998 Cu—4.88Ni—1.24Si  900° C. - 1 minute 12.9 J999Cu—5.39Ni—1.35Si  900° C. - 2 minute 14.1 K001 Cu—1.65Ni—0.82Si—1.66Co1000° C. - 30 seconds 12.9 K002 Cu—2.56Ni—0.80Si—0.79Co  950° C. - 1minute 17.7 K003 Cu—2.45Ni—1.23Si—2.46Co 1000° C. - 30 seconds 6.7 K004Cu—3.70Ni—1.22Si—1.15Co 1000° C. - 30 seconds 12.9 K009Cu—1.74Ni—0.78Si—1.67Mn  850° C. - 30 seconds 28.2 K010Cu—2.65Ni—0.79Si—0.79Mn  850° C. - 30 seconds 22.1 K011Cu—2.51Ni—1.19Si—2.56Mn  850° C. - 1 minute 9.1 K012Cu—3.70Ni—1.21Si—1.19Mn  850° C. - 1 minute 9.8 K013Cu—3.22Ni—0.81Si—0.10Cr  850° C. - 1 minute 12.6 K014Cu—3.31Ni—0.82Si—0.18Cr  850° C. - 1 minute 10.7 K015Cu—4.82Ni—1.21Si—0.09Cr  900° C. - 1 minute 15.5 K016Cu—4.89Ni—1.26Si—0.18Cr  900° C. - 1 minute 12.9 K036Cu—3.69Ni—0.73Si—0.52Sn  850° C. - 2 minute 10.3 K037Cu—3.66Ni—0.77Si—0.93Sn  850° C. - 2 minute 16.2 K040Cu—3.74Ni—0.72Si—0.08Mg  850° C. - 2 minute 17.7 K041Cu—3.78Ni—0.76Si—0.205Mg  850° C. - 2 minute 18.6

TABLE 3 Properties of the Alloys from Examples 1 from SA-age-CR-ageprocess YS/TS/EI Alloy Ages % IACS ksi/ksi/% 90° MBR/t J994 450/300 36.8126.7/130.8/2 2.9/3.4 J995 450/300 35.5 130.8/134.7/1 3.2/6.7 J996450/300 34.5 132.7/138.5/2 3.1/6.9 J997 450/300 33.7 135.3/139.3/23.7/6.7 J998 450/300 34.3 137.9/144.2/2 3.3/8.6 J999 450/300 34.2140.9/147.1/2 3.4/6.7 K001 500/300 40.3 129.2/134.4/2 — K002 500/35040.5 130.3/135.8/2 3.8/5.2 K003 450/300 37.8 129.7/134.3/2 3.5/3.7 K004450/300 28.4 145.3/150.8/2 5.1/6.8 K009 450/350 16.5 108.1/113.3/4 —K010 450/300 22.9 127.1/131.3/2 — K011 400/300 11.9 137.6/141.0/22.4/3.2 K012 400/300 17.0 135.4/140.4/2 2.4/3.7 K013 450/300 36.7125.4/129.6/2 — K014 450/300 36.2 128.0/131.9/2 — K015 450/300 33.8135.6/139.8/2 3.5/5.2 K016 450/300 32.4 136.0/140.4/2 3.3/5.2 K036450/300 34.3 131.5/143.1/1 3.9/6.9 K037 450/300 30.8 135.2/147.1/23.5/6.8 K040 450/350 38.4 125.4/136.5/2 — K041 450/350 37.7123.7/135.5/1 —

Example 2 Cobalt Improves Strength

Selected alloys of Example 1 were solution heat treated in a fluidizedbed furnace for the time and temperature listed in Table 2. FIG. 2 is aflow chart of the process of this Example 2. Subsequently the alloyswere cold rolled 25% to 0.009″ then subjected to an aging anneal of 400°to 500° C. for 3 hours. After an additional cold reduction of 22% to0.007″, samples were aged annealed at temperatures of 300° to 400° C.for 3 hours. Properties from representative conditions are listed inTable 4. Bend properties in many cases are somewhat better at similarstrengths than the process in Example 1. Co (K003 and K004) and Sn(K037) additions provide the highest strength increase of the alloys inthis example.

TABLE 4 Properties of the Examples 2 from SA-CR-age-CR-age processYS/TS/EI Alloy Ages % IACS ksi/ksi/% 90° MBR/t J994 450/300 38.3130.0/134.3/2 2.3/3.7 J997 450/300 37.7 125.2/132.7/2 2.9/8.9 J998400/300 28.8 128.4/134.0/2 3.1/4.0 J999 400/300 29.5 131.9/135.4/23.1/5.1 K002 450/300 35.1 125.0/129.2/1 2.4/4.9 K003 450/300 33.7135.2/140.3/2 3.1/4.0 K004 450/300 31.9 134.4/139.7/2 3.7/6.7 K014450/300 38.1 127.9/132.3/2 2.3/4.0 K036 450/300 36.0 129.2/131.8/13.1/3.9 K037 450/300 32.0 135.2/139.8/2 3.3/4.7 K040 450/300 38.7127.1/129.3/1 — K041 450/300 38.4 132.4/136.4/1 3.6/4.7

Example 3 Cobalt and Chromium Levels and (Ni+Co)/(Si−Cr/5) Ratio

A series of ten pound laboratory ingots with the compositions listed inTable 5 were melted in a silica crucible and Durville cast into steelmolds, which after gating were approximately 4″×4″×1.75″. FIG. 3 is aflow chart of the process of this Example 3. After soaking two hours at900° C. they were hot rolled in three passes to 1.1″ (1.6″/1.35″/1.1″),reheated at 900° C. for 10 minutes, and further hot rolled in threepasses to 0.50″ (0.9″/0.7″/0.5″), followed by a water quench. Thequenched plates were then soaked at 590° C. for 6 hours, trimmed andthen milled to remove surface oxides developed during hot rolling. Thealloys were then cold rolled to 0.012″ and solution heat treated in afluidized bed furnace for 60 seconds at the temperatures listed in Table5. The temperature was selected to maintain a fairly constant grainsize. Alloys were then subjected to an aging anneal of 400° to 500° C.for 3 hours, designed to increase strength and conductivity. The alloyswere then cold rolled 25% to 0.009″ and aged at 300° to 400° C. for 4hours. Properties measured after the second age anneal are presented inTable 6. From this data set, it can be observed that additions to a baseAlloy of Cu—Ni—Si of Co (K068), Cr (K072), or both Co and Cr (K070)achieve the best combinations of strength, conductivity and bendformability. It is also noted that relatively high Si levels of 1.2% andabove were present in the samples with the highest strength. While therewas some evidence of strengthening from Sn, this was accompanied by poorbend formability. In Table 5, it can be seen that the ratio(Ni+Co)/(Si−Cr/5) is very close to 4 for most of the alloys,particularly K068, K070 and K072. Also, the Ni/Co ratio was close to 3for K068 and K070. Yield strength is plotted against conductivity inFIG. 4, and against bend formability in FIG. 5. The values for K068,K070 and K072 are identified to show their unusually good combination ofproperties.

TABLE 5 Alloys of Examples 3 and 4 (Ni + Co)/ Solution Anneal GrainSize, Alloy Analyzed composition, wt % (Si − Cr/5) Ratio Ni/CoTemperature μm K056 Cu—4.94Ni—0.97Si—0.86Sn 5.09 900° C. 15 K057Cu—2.63Ni—0.73Co—0.80Si—0.88Sn 4.20 3.60 925° C. 16 K058Cu—3.80Ni—0.97Co—1.24Si—0.83Sn 3.85 3.92 950° C. 14 K059Cu—3.27Ni—0.82Si—0.22Mn 3.99 850° C. 20 K061Cu—3.83Ni—1.28Co—1.27Si—0.31Mn 4.02 2.99 950° C. 8 K065Cu—4.96Ni—1.25Si—0.085Mg 3.97 900° C. 17 K066Cu—3.29Ni—0.84Si—0.33Mn—0.092Mg 3.92 850° C. 10 K067Cu—2.57Ni—0.83Co—0.83Si—0.082Mg 4.10 3.10 950° C. 21 K068Cu—3.80Ni—1.21Co—1.27Si—0.048Mg 3.94 3.14 975° C. 12 K069Cu—3.42Ni—0.84Si—0.89Sn—0.062Mg 4.07 875° C. 28 K070Cu—3.83Ni—1.29Co—1.39Si—0.56Cr 4.01 2.97 975° C. 8 K071Cu—3.36Ni—0.95Si—0.54Cr—0.035Mg 3.99 950° C. 19 K072Cu—4.64Ni—1.28Si—0.54Cr—0.078Mg 3.96 950° C. 17 K073Cu—3.52Ni—1.07Si—1.06Cr—0.047Mg 4.10 950° C. 14 K074Cu—4.11Ni—1.31Si—1.01Cr—0.058Mg 3.71 975° C. 18 K075Cu—4.71Ni—1.29Si—0.50Cr—0.85Sn 3.96 950° C. 19 K076 Cu—3.54Ni—1.00Si—0.49Cr—0.89Sn 3.92 925° C. 17

TABLE 6 Properties from SA-age-CR-age process of Example 3 YS/TS/EIAlloy Ages % IACS ksi/ksi/% 90° MBR/t K056 450/300 25.7 142.7/148.4/28.7/8.7 K057 450/350 29.0 131.3/137.6/3 3.3/6.9 K058 450/300 24.5142.8/149.0/2 5.2/6.9 K059 450/350 32.2 132.3/137.5/3 2.9/2.9 K061450/350 27.2 142.0/146.5/2 3.6/5.2 K065 450/300 32.4 137.8/143.1/16.9/6.9 K066 450/350 29.1 134.5/139.8/2 3.1/3.1 K067 500/300 38.6132.4/137.0/2 3.8/5.2 K068 450/300 28.6 143.2/149.3/2 4.0/6.9 K069450/350 30.3 134.1/139.4/3 4.0/6.9 K070 450/350 31.0 147.1/151.9/24.0/4.0 K071 450/350 33.5 134.9/140.0/3 3.1/3.3 K072 450/350 30.6145.7/151.1/2 4.0/6.9 K073 450/350 33.8 141.6/146.6/2 3.8/4.0 K074450/350 29.4 146.9/153.1/2 3.8/6.9 K075 450/350 26.2 145.4/152.9/35.2/8.7 K076 450/350 27.7 137.7/144.8/3 3.1/6.9

Example 4 Cobalt and Chromium for Strength and Formability

The alloys of Example 3 were solution heat treated in a fluidized bedfurnace for 60 seconds at the temperature listed in Table 5. FIG. 6 is aflow chart of the process of this Example 4. Subsequently the alloyswere cold rolled 25% to 0.009″ then subjected to an aging anneal of 400°to 500° C. for 3 hours. After an additional cold reduction of 22% to0.007″, samples were aged annealed at temperatures of 300° to 400° C.for 3 hours. Properties from representative conditions are listed inTable 7. Similar to Example 3, of particular note are alloys K068, K070and K072, which show that alloys containing Co, Cr or a combination ofboth achieve the highest strength levels. The bend formability dataindicates that K068 and K070 which both contain Co have the bestformability at higher strength. Yield strength is plotted againstconductivity in FIG. 7, and against bend formability in FIG. 8. Thevalues for alloys K068, K070 and K072 are noted.

TABLE 7 Properties from SA-CR-age-CR-age process of the Alloys ofExhibit 4 YS/TS/EI Alloy Ages % IACS ksi/ksi/% 90° MBR/t K056 450/30029.1 147.4/152.4/2 5.7/8.6 K057 450/300 29.7 136.1/141.9/2 2.0/5.7 K058450/300 25.6 146.7/153.3/1 2.0/8.6 K065 450/300 34.7 142.9/145.4/23.6/4.9 K067 500/300 38.4 137.4/141.7/3 2.9/5.7 K068 450/300 30.3151.6/155.3/1 3.6/4.9 K069 450/300 29.7 139.4/145.7/1 2.9/8.6 K070450/300 31.1 152.3/157.9/2 2.9/3.9 K071 450/300 34.8 143.8/147.6/22.9/3.9 K072 450/300 31.4 155.4/161.3/1 2.7/8.6 K073 450/300 34.7147.2/150.9/2 2.7/3.9 K074 450/300 29.8 153.9/160.0/1 2.1/3.9 K075450/300 26.5 151.4/158.2/2  2.0/11.0 K076 450/300 28.1 142.8/149.0/12.1/8.6

Example 5 Nickel:Cobalt Ratio

A series of ten pound laboratory ingots with the compositions listed inTable 8 were melted in a silica crucible and Durville cast into steelmolds, which after gating were approximately 4″×4″×1.75″. FIG. 9 is aflow chart of the process of this Example 5. This group of alloys wasbased on K068, K070 and K072 from Table 5, wherein overall alloyinglevel and Ni/Co ratio were varied while keeping the stoichiometric ratio((Ni+Co)/(Si−Cr/5)) close to 4.2. After soaking two hours at 900° C.they were hot rolled in three passes to 1.1″ (1.6″/1.35″/1.1″), reheatedat 900° C. for 10 minutes, and further hot rolled in three passes to0.50″ (0.9″/0.7″/0.5″), followed by a water quench. The quenched plateswere then soaked at 590° C. for 6 hours, trimmed and then milled toremove surface oxides developed during hot rolling. The alloys were thencold rolled to 0.012″ and solution heat treated in a fluidized bedfurnace for 60 seconds at the temperature listed in Table 8. Thetemperature was selected to maintain a fairly constant grain size.Alloys were then subjected to an aging anneal of 450° to 500° C. for 3hours, designed to increase strength and conductivity. The alloys werethen cold rolled 25% to 0.009″ and aged at 300 to 400° C. for 4 hours.Properties measured after the second age anneal for the process with a475° C. first age and 300° C. second age are presented in Table 9. Forthe Co-only set of compositions (K077 to K085), yield strength valuestend to increase with higher alloying content. For example, K078, with aNi+Co+Cr+Si value of 6.24, had a yield strength of 155 ksi while K084with a Ni+Co+Cr+Si value of 5.22 had a 139 ksi yield strength. A Ni/Coratio of 3 to 4 provides better strength than a ratio of 5, when onecompares K077 (Ni/Co ratio of 3.62) and K078 (Ni/Co ratio of 3.83) toK079 (Ni/Co ratio of 5.04), as well as comparing K080 (Ni/Go ratio of3.32) and K081 (Ni/Co ratio of 3.93) to K082 (Ni/Co ratio of 4.89). Theplots of yield strength vs Ni/Co ratio in FIG. 10 illustrate this, withthe exception of K085, which has a higher Si level than K083 and K084.The Co-and-Cr-containing alloys, K086 to K094, were not as sensitive tooverall alloying levels and Ni/Co ratio as the Co-only alloys. TheCr-only alloys (K095 to K097) also had comparable properties to theother alloy types.

TABLE 8 Alloys of Example 5 (Ni + Co)/(Si − Solution Anneal Grain Size,Alloy Analyzed composition, wt % Ni/Co Ni + Co + Cr + Si Cr/5) RatioTemperature, ° C. μm K077 Cu—3.84Ni—1.06Co—1.31Si 3.62 6.21 3.740 97510.0 K078 Cu—3.98Ni—1.04Co—1.22Si 3.83 6.24 4.115 975 10.3 K079Cu—4.28Ni—0.85Co—1.32Si 5.04 6.45 3.886 975 14.8 K080Cu—3.49Ni—1.05Co—1.10Si 3.32 5.64 4.127 975 15.5 K081Cu—3.77Ni—0.96Co—1.17Si 3.93 5.90 4.043 975 16.9 K082Cu—3.86Ni—0.79Co—1.12Si 4.89 5.77 4.152 975 20.4 K083Cu—3.22Ni—1.05Co—1.06Si 3.07 5.33 4.028 975 15.5 K084Cu—3.33Ni—0.89Co—1.00Si 3.74 5.22 4.220 950 15.3 K085Cu—3.59Ni—0.75Co—1.16Si 4.79 5.50 3.741 950 18.7 K086Cu—3.80Ni—1.20Co—1.46Si—0.57Cr 3.17 7.03 3.715 975 10.9 K087Cu—4.03Ni—1.01Co—1.37Si—0.60Cr 3.99 7.01 4.032 975 15.9 K088Cu—4.26Ni—0.82Co—1.51Si—0.57Cr 5.20 7.16 3.639 975 16.4 K089Cu—3.50Ni—1.11Co—1.33Si—0.58Cr 3.15 6.52 3.797 975 10.5 K090Cu—3.75Ni—0.92Co—1.25Si—0.55Cr 4.08 6.47 4.096 975 16.3 K091Cu—3.97Ni—0.79Co—1.42Si—0.56Cr 5.03 6.74 3.639 975 16.7 K092Cu—3.25Ni—1.01Co—1.22Si—0.58Cr 3.22 6.06 3.859 975 15.2 K093Cu—3.43Ni—0.86Co—1.30Si—0.51Cr 3.99 6.10 3.581 975 16.0 K094Cu—3.50Ni—0.73Co—1.22Si—0.59Cr 4.79 6.04 3.838 975 17.5 K095Cu—4.97Ni—1.36Si—0.60Cr 6.93 4.008 950 18.4 K096 Cu—4.63Ni—1.35Si—0.61Cr6.59 3.770 925 12.0 K097 Cu—4.20Ni—1.18Si—0.59Cr 5.97 3.955 925 18.9

TABLE 9 Properties from SA-age-CR-age process of Example 5 YS/TS/EIAlloy Ages % IACS ksi/ksi/% 90° MBR/t K077 475/300 29.1 152.1/159.3/45.2/5.2 K078 475/300 29.7 155.5/162.3/4 5.2/5.2 K079 475/300 30.7143.7/150.1/4 K080 475/300 31.2 142.4/147.9/3 5.2/3.6 K081 475/300 30.7144.2/148.3/3 4.0/6.1 K082 475/300 32.2 137.7/142.7/2 K083 475/300 31.1140.0/145.8/3 5.2/5.2 K084 475/300 32.1 138.9/145.6/3 K085 475/300 31.8140.4/146.3/2 K086 475/300 30.1 151.6/157.9/4 5.2/6.1 K087 475/300 30.5149.4/153.6/3 5.2/3.6 K088 475/300 30.4 152.2/159.3/4 5.2/5.2 K089475/300 30.3 149.0/155.6/3 4.0/5.2 K090 475/300 31.3 151.9/157.4/35.2/3.8 K091 475/300 30.7 149.5/154.5/3 5.2/6.1 K092 475/300 30.8146.5/152.1/3 4.0/5.2 K093 475/300 30.3 147.2/153.4/4 5.2/5.2 K094475/300 31.2 148.1/154.4/2 4.0/3.8 K095 475/300 30.7 150.2/159.1/33.8/6.1 K096 475/300 32.1 153.3/160.6/4 4.0/6.1 K097 475/300 31.9148.7/155.5/3 3.8/5.2

The alloys of Table 8 were solution heat treated in a fluidized bedfurnace 60 seconds at the temperature listed in Table 8. Subsequentlythe alloys were cold rolled 25% to 0.009″ then subjected to an aginganneal of 450 to 500° C. for 3 hours. After an additional cold reductionof 22% to 0.007″ samples were aged annealed at temperatures of 300 to400° C. for 3 hours. Properties from samples given first and second agesat 450° C. and 300° C., respectively, are listed in Table 10. TheCo-only alloys displayed a sensitivity to overall alloying levels withthis scheme which was not found in alloys containing Cr. The onlyCo-only alloys at 150 ksi yield strength and above were K077 and K078,while all Cr-containing alloys reached or came close to that strengthlevel. Strength-bend properties for this process are fairly similar tothose in Table 9.

TABLE 10 Properties from SA-CR-age-CR-age process of Example 5 YS/TS/EIAlloy Ages % IACS ksi/ksi/% 90° MBR/t K077 450/300 29.1 152.8/160.2/23.7/4.3 K078 450/300 30.1 149.7/157.7/4 4.0/4.9 K079 450/300 35.2133.4/140.3/2 K080 450/300 32.2 133.1/139.6/2 K081 450/300 32.2133.0/138.8/2 K082 450/300 44.9 100.7/112.9/3 K083 450/300 30.2140.7/145.8/3 K084 450/300 31.8 141.7/146.7/3 4.0/5.1 K085 450/300 31.2141.4/146.7/2 K086 450/300 30.3 150.8/156.6/2 4.9/6.7 K087 450/300 30.2153.4/158.7/2 4.6/4.9 K088 450/300 28.6 153.7/159.4/2 3.7/6.7 K089450/300 29.8 148.9/155.4/1 4.6/6.7 K090 450/300 29.9 151.3/155.9/34.6/4.3 K091 450/300 30.0 152.4/159.5/1 4.0/6.7 K092 450/300 32.5149.6/156.4/3 4.3/6.7 K093 450/300 30.3 147.1/152.7/2 4.6/6.7 K094450/300 29.9 150.4/156.9/2 4.3/4.9 K095 450/300 30.0 155.9/165.3/24.0/6.7 K096 450/300 31.8 157.5/165.4/3 4.0/6.7 K097 450/300 32.0155.1/161.6/3 4.3/4.9

Example 6 Nickel:Cobalt Ratio

Laboratory ingots with the compositions listed in Table 11 were meltedin a graphite crucible and Tamman cast into steel molds, which aftergating were 4.33″×2.17″×1.02″. FIG. 11 is a flow chart of the process ofthis Example 6. For a target Si-content of 1% and Cr-content of 0.5% onealloy is Co-containing and the other is Co-free, the Ni-content isadjusted in order to keep a stoichiometric ratio ((Ni+Co)/(Si−Cr/5)) ofclose to 4.2. After soaking two hours at 900° C. they were hot rolled to0.472″, thereby reheated after each pass at 900° C. for 10 minutes.After the last pass the bar was water quenched. After trimming andmilling to 0.394″ in order to remove the surface oxide, the alloys werecold rolled to 0.0106″ and solution heat treated in a fluidized bedfurnace for the time and temperature listed in Table 11. Time andtemperature were selected to achieve grain sizes below 20 μm. The alloyswere then subjected to an aging anneal of 450 to 500° C. for 3 hours,designed to increase strength and conductivity. The alloys were thencold rolled 25% to 0.0079″ and aged at 300 or 400° C. for 3 hours.Properties measured after the second age anneal are presented in Table12. The formability was measured via V-block. The data indicates thatboth alloys are capable of achieving a yield strength of 135 ksi, yetthe Co-containing variant BS shows a better softening resistance thatcan be seen with increasing the age annealing temperature. The slightlybetter bad way bendability of variant BS is presumably due to theslightly lower grain size after solution annealing.

TABLE 11 Alloys of Example 6, wt. % (Ni + Co)/(Si − Grain alloy Ni Co CrSi Mg Cr/5) Ratio* Ni/Co SA conditions size, μm BR 3.59 0.48 1.00 3.97 ∞915° C. - 1 10-15 minute BS 3.18 0.47 0.49 0.97 4.19 6.77 950° C. - 1 5-10 minute

TABLE 12 Properties from SA-age-CR-age Process of Example 6 1.AA 2.AA300° C./3 h 2AA 400° C./3 h Temp 90° 90° Alloy ° C. YS ksi TS ksi A10% %IACS MINBR/ YS ksi TS ksi A10% % IACS MINBR/ BR 450 135.8 144.2 3.7 32.54.0/5.0 118.2 129.5 6.5 37.1 —/— 475 133.9 141.8 3.7 35.1 4.0/6.0 124.0132.9 7.9 38.5 —/— 500 117.3 123.6 5 37.1 4.0/4.0 100.1 108.8 11 41.6—/— BS 450 135.8 142.6 1.8 31.7 4.0/4.0 128.2 137.2 3.7 33.5 3.5/4.0 475132.7 138.4 1.7 34.6 5.0/5.5 126.5 136.2 2.3 38.3 4.0/4.5 500 127.3134.7 4.8 37.4 4.0/5.0 119.4 127.8 6 41.2 —/—

Example 7 (Ni+Co)/(Si−Cr/5) Ratio

A group of alloys was cast and processed using once more the basiccompositions of K068 (Co only), K070 (Co and Cr) and K072 (Cr only) fromTable 5 as a base, but in this case with a gradual drop in Si levels,thus increasing the (Ni+Co)/(Si−Cr/5) stoichiometric ratio above the 3.6to 4.2 range of previous alloys. Ni and Co levels were designed to beconstant for each of the three alloy types. A series of ten poundlaboratory ingots with the compositions listed in Table 11 were meltedin a silica crucible and Durville cast into steel molds, which aftergating were approximately 4″×4″×1.75″. K143 to K146 are variants ofK072, K160 to K163 variants of K070, and K164 to K167 are variants ofK068. FIG. 12 is a flow chart of the process of this Example 7. Aftersoaking two hours at 900° C. they were hot rolled in three passes to1.1″ (1.6″/1.35″/1.1″), reheated at 900° C. for 10 minutes, and furtherhot rolled in three passes to 0.50″ (0.9″/0.7″/0.5″), followed by awater quench. The quenched plates were then soaked at 5900° C. for 6hours, trimmed and then milled to remove surface oxides developed duringhot rolling. The alloys were then cold rolled to 0.012″ and solutionheat treated in a fluidized bed furnace for 60 seconds at thetemperatures listed in Table 13. The temperature was selected tomaintain a fairly constant grain size. The alloys were then cold rolled25% to 0.009″ and aged 450, 475 and 500° C. for 3 hours. Propertiesafter each aging temperature for alloys of the current example, as wellas K068, K070, K072, K078, K087 and K089 are listed in Table 14. Foreach alloy type, yield strength decreases as the stoichiometric ratioincreases above about 4.5, and fails below 120 ksi at a ratio of around5.5. This is shown in FIGS. 13 to 15 for the Cr alloys (plus K072 data),the Co-alloys (plus K068 and K078 data), and the Co—Cr alloys (plusK070, K087 and K089 data), respectively. In the Co and Cr alloys,conductivity decreases as the stoichiometric ratio increases above about4.5, while for the alloys with both Co and Cr there is not a clearrelationship between stoichiometry and conductivity. This is showngraphically in FIGS. 16 through 18. Based on this data it is evidentthat the best yield strength-conductivity properties are produced whenthe stoichiometric ratio is kept between 3.5 and 5.0.

TABLE 13 Alloys of Example 7 (Ni + Co)/ (Si − Cr/5) SA alloy Ni Co Cr SiMg Ratio Ni/Co Temperature K143 4.61 0.519 1.11 0.099 4.582 950 K1444.63 0.503 0.828 0.074 6.365 950 K145 4.59 0.607 0.91 0.085 5.820 950K146 4.55 0.576 0.803 0.093 6.615 950 K160 3.84 1.2 0.52 1.19 4.641 3.20975 K161 3.8 1.18 0.515 1.1 4.995 3.22 975 K162 3.83 1.2 0.513 1.035.424 3.19 975 K163 3.84 1.21 0.556 0.938 6.108 3.17 975 K164 3.74 1.171.05 0.104 4.676 3.20 975 K165 3.9 1.23 1.01 0.116 5.079 3.17 975 K1663.87 1.23 0.918 0.12 5.556 3.15 975 K167 3.9 1.24 0.83 0.085 6.193 3.15975

TABLE 14 Properties after solution annealing, cold rolling 25% and agingof Example 7 450° C. age 475° C. age 500° C. age alloy YS, ksi % IACS90° bends YS, ksi % IACS 90° bends YS, ksi % IACS 90° bends K143 138.931.2 2.9/2.0 135.8 33.7 2.0/2.7 126.3 35.8 2.0/2.2 K144 118.1 27.51.8/2.2 125.6 30.8 1.3/1.1 121.3 33.1 2.2/1.3 K145 120.8 27.3 2.0/1.3127.5 30.3 2.2/1.3 123.5 32.6 2.2/1.8 K146 113.4 26.8 1.8/1.1 121.7 30.42.2/2.0 116.8 32.2 1.3/1.6 K160 127.4 29.5 2.0/3.1 133.8 34.0 2.4/1.6122.6 39.3 1.8/1.8 K161 127.4 29.4 2.4/1.1 131.3 33.0 2.2/1.6 123.5 35.71.8/0.7 K162 122.4 33.4 1.3/1.3 120.7 34.4 2.4/1.3 116.5 35.9 1.6/1.3K163 120.7 29.8 1.3/1.1 119.4 32.0 1.6/1.1 111.1 34.2 1.6/1.1 K164 126.629.9 2.4/1.6 132.6 33.7 2.4/2.0 125.8 36.7 2.0/2.9 K165 118.9 29.62.2/1.6 124.0 32.9 2.2/2.4 119.5 35.4 1.6/1.8 K166 116.6 27.9 2.0/1.3120.4 30.4 2.9/1.1 117.7 32.5 2.0/1.8 K167 111.6 25.7 2.0/1.6 114.5 27.41.6/1.3 113.4 29.3 1.3/0.2 K068 131.9 29.3 2.2/2.8 131.7 33.5 2.2/2.2K070 134.7 29.7 2.2/1.6 129.7 33.6 1.7/1.6 K072 133.3 29.9 1.7/1.7 130.033.2 1.6/2.2 K078 125.3 30.8 — 133.3 31.9 2.2/1.6 125.7 36.3 — K087133.4 29.0 — 136.9 30.7 2.2/1.6 124.1 37.7 — K089 136.2 29.9 — 135.030.6 — 131.5 34.4 —

Example 8 (Ni+Co)/(Si−Cr/5) Ratio

A series of ten pound laboratory ingots with the compositions listed inTable 15 were melted in a silica crucible and Durville cast into steelmolds, which after gating were approximately 4″×4″×1.75″. FIG. 19 is aflow chart of the process of this Example 8. After soaking two hours at900° C. they were hot rolled in three passes to 1.1″ (1.6″/1.35″/1.1″),reheated at 900° C. for 10 minutes, and further hot rolled in threepasses to 0.50″ (0.9″/0.7″/0.5″), followed by a water quench. Thequenched plates were then soaked at 590° C. for 6 hours, trimmed andthen milled to remove surface oxides developed during hot rolling. Thealloys were then cold rolled to 0.012″ and solution heat treated in afluidized bed furnace for 60 seconds at 950° C. Grain size ranged from 6to 12 μm. Alloys were then subjected to an aging anneal of 450 or 475°C. for 3 hours, designed to increase strength and conductivity. Thealloys were then cold rolled 25% to 0.009″ and aged at 300° C. for 4hours. Properties measured after the second age anneal are presented inTable 16.

Table 17 has properties measured after samples were solution heattreated in a fluidized bed furnace for 60 seconds at 950° C., coldrolled 25% to 0.009″, given an aging anneal at 475° C. for 3 hours, coldrolled 22% to 0.007″, and given a final anneal of 300° C. for 3 hours.The results show the viability of a range of compositions with Si from1.0 to 1.2%, with a Ni/Co ratio of 4, and a stoichiometric ratio(((Ni+Co)/(Si−Cr/5))) of 3.5 to 5.0. This is shown graphically in FIGS.20 and 21, which plot conductivity and yield strength data from Table 17versus the stoichiometric ratio. These plots show yield strengths of 140ksi or higher combined with conductivities of 25% IACS or higher areobtained for this process when the ratio is between 3.0 and 5.0. Cr wasnot found to influence properties significantly in the alloys of thisexample.

Stress relaxation tests were run on samples of K188 and K205 which werecold rolled to 0.012″ from milled hot rolled plate, solution annealed at950° C. for 60 seconds, cold rolled 25% to 0.009″, and age annealed at475° C. for 3 hours. The stress relaxation tests were run at 150° C. for3000 hours on samples of longitudinal and transverse orientation.Results in Table 18 show that both alloys had excellent stressrelaxation resistance, over 85% stress remaining after 1000 hours at150° C., regardless of Cr content or sample orientation.

TABLE 15 Alloys of Example 8 Alloy Analyzed composition, wt % Ni/CoStoichiometric ratio Grain Size, μm K188Cu—3.40Ni—0.81Co—1.16Si—0.42Cr—0.019Mg 4.20 3.91 7.3 K189Cu—3.20Ni—0.72Co—1.05Si—0.38Cr—0.033Mg 4.46 4.02 10.1 K190Cu—3.22Ni—0.70Co—1.28Si—0.31Cr—0.036Mg 4.59 3.22 8.5 K191Cu—3.22Ni—0.70Co—1.05Si—0.53Cr—0.064Mg 4.58 4.16 9.5 K192Cu—2.94Ni—0.69Co—1.29Si—0.55Cr—0.062Mg 4.24 3.08 10.9 K193Cu—3.21Ni—0.90Co—1.05Si—0.34Cr—0.117Mg 3.56 4.18 8.6 K194Cu—3.20Ni—0.84Co—1.30Si—0.22Cr—0.035Mg 3.80 3.22 7.8 K195Cu—3.18Ni—0.86Co—0.81Si—0.52Cr—0.070Mg 3.71 5.72 7.1 K196Cu—3.19Ni—0.89Co—1.28Si—0.57Cr—0.111Mg 3.60 3.49 7.7 K197Cu—3.61Ni—0.70Co—1.06Si—0.36Cr—0.067Mg 5.14 4.36 10.7 K198Cu—3.60Ni—0.70Co—1.28Si—0.39Cr—0.077Mg 5.13 3.58 8.7 K199Cu—3.60Ni—0.70Co—1.06Si—0.60Cr—0.076Mg 5.13 4.58 9.3 K200Cu—3.60Ni—0.70Co—1.28Si—0.60Cr—0.092Mg 5.14 3.70 9.3 K201Cu—3.63Ni—0.88Co—1.04Si—0.29Cr—0.065Mg 4.12 4.59 6.0 K202Cu—3.62Ni—0.90Co—1.27Si—0.36Cr—0.101Mg 4.04 3.77 7.4 K203Cu—3.59Ni—0.89Co—1.05Si—0.56Cr—0.076Mg 4.04 4.77 6.1 K204Cu—3.58Ni—0.88Co—1.27Si—0.56Cr—0.075Mg 4.09 3.85 5.9 K205Cu—3.73Ni—0.91Co—1.13Si—0.082Mg 4.09 4.11 12.1 K206Cu—3.53Ni—0.81Co—1.02Si—0.080Mg 4.36 4.25 12.2 K207Cu—3.53Ni—0.78Co—1.25Si—0.055Mg 4.55 3.44 9.9 K208Cu—3.57Ni—1.00Co—1.02Si—0.070Mg 3.57 4.48 7.6 K209Cu—3.54Ni—1.02Co—1.25Si—0.085Mg 3.47 3.65 7.4 K210Cu—3.94Ni—0.82Co—1.06Si—0.149Mg 4.78 4.49 9.5 K211Cu—3.97Ni—0.80Co—1.24Si—0.065Mg 4.97 3.85 11.5 K212Cu—3.95Ni—0.99Co—1.04Si—0.100Mg 4.01 4.75 10.2 K213Cu—3.97Ni—0.99Co—1.22Si—0.079Mg 4.01 4.07 10.2

TABLE 16 SA-age-CR-age process properties of Example 8 YS/TS/EI AlloyAges % IACS ksi/ksi/% 90° MBR/t K188 450/300 29.3 149.5/156.1/2 3.3/5.2K189 475/300 33.6 147.3/153.8/2 4.0/4.0 K204 450/300 29.7 149.6/155.1/24.0/5.2 K205 475/300 34.2 149.8/155.7/2 4.0/5.2 K206 475/300 35.0147.9/153.9/2 4.0/5.3 K213 475/300 34.2 150.8/157.4/2 5.2/5.2

TABLE 17 SA-CR-age-CR-age process properties of Example 8 YS/TS/EI AlloyAges % IACS ksi/ksi/% 90° MBR/t K188 475/300 35.1 145.7/152.4/3 2.0/4.9K189 475/300 34.7 146.1/152.6/2 2.6/5.7 K190 475/300 28.0 139.2/148.5/42.9/5.1 K191 475/300 37.2 143.7/149.9/3 3.4/6.7 K192 475/300 28.1139.7/146.4/2 2.6/6.7 K193 475/300 36.2 143.6/149.3/3 2.9/5.1 K194475/300 29.1 138.7/146.1/3 2.6/6.7 K195 475/300 35.5 130.7/134.7/42.0/3.4 K196 475/300 30.2 143.4/149.5/2 2.6/9.0 K197 475/300 35.4145.3/152.0/2 3.1/6.7 K198 475/300 31.7 148.2/155.7/3 2.9/6.7 K199475/300 35.5 147.8/154.4/3 2.9/9.0 K200 475/300 33.7 146.3/152.9/33.4/6.7 K201 475/300 36.8 145.2/150.0/2 2.9/6.7 K202 475/300 33.5146.1/152.8/3 2.6/5.1 K203 475/300 34.4 147.4/153.6/2 3.6/5.7 K204475/300 33.9 150.3/156.8/3 2.9/6.7 K205 475/300 35.3 147.0/152.8/22.9/5.7 K206 475/300 35.8 146.9/153.7/3 2.4/6.7 K207 475/300 29.7143.3/150.3/2 2.6/6.7 K208 475/300 36.2 142.5/148.1/3 2.9/6.7 K209475/300 32.2 145.5/152.1/3 2.6/6.7 K210 475/300 34.1 148.6/154.1/52.9/6.7 K211 475/300 33.8 144.7/152.1/2 3.1/5.1 K212 475/300 34.5140.6/145.4/3 2.9/5.7 K213 475/300 35.0 148.4/154.4/2 3.6/6.7

TABLE 18 150° C. Stress Relaxation Data for samples cold rolled 25% andaged at 475° C. for 3 hours of Example 8 Longitudinal Transverse (inpercent (in percent Yield Strength, stress remaining) stress remaining)Alloy ksi 1000 hr 3000 hr 1000 hr 3000 hr K188 (Cr) 136.4 89.9 87.9 88.285.2 K205 (no Cr) 132.2 92.0 90.4 91.6 89.6

Example 9 Effect of Cr

A series of ten pound laboratory ingots with the compositions listed inTable 19 were melted in a silica crucible and Durville cast into steelmolds, which after gating were approximately 4″×4″×1.75″. FIG. 22 is aflow chart of the process of this Example 9. The ingots were thenmachined to have tapered edges, as illustrated schematically in FIG. 23,to create a higher state of tensile stress at the edges. This conditionis more prone to edge cracking than the standard flat edges, and thusmore sensitive to alloying additions, in this case Cr. The alloys weresoaked for two hours at 900° C., and rolled in two passes to 1.12″(1.4″/1.12″) then water quenched. After examination for cracks, the barswere reheated at 900° C. for two hours, and rolled in three passes to0.50″ (0.9″/0.7″/0.5″), followed by a water quench. It was found thatwithout Cr, K224 developed large cracks during the first few passes ofhot rolling, which enlarged during the remaining passes. None of theCr-containing alloys developed large cracks during hot rolling. A few ofthe alloys showed small cracks after initial passes believed to be dueto casting defects, but these did not enlarge during subsequent passes.The Cr effect was the same independent of Cr level, from 0.11% to 0.55%.Examples of edge conditions of K224 and K225 after hot rolling are shownin FIGS. 24 and 25. The addition of even a small amount of Cr wouldreduce cracking in plant production, thus improving yield after hotrolling and coil milling Data from plant-cast bars (i.e., bars cast aspilot product dc castings), whose compositions are listed in Table 20,show the beneficial effect of Cr on preventing hot rolling cracks andtherefore improving yield. Table 21 lists the normalized casting plantyield (CPY) of six Cr-containing and four non-Cr bars, where thenormalized CPY is obtained as follows: First the individualized CPY iscalculated as the ratio of coil milled weight to cast bar weight. Secondthe bar with the highest CPY, in this case RN 033410, is assigned anormalized CPY of 100%. Third the normalized CPY of all other bars iscalculated by dividing the CPY of each bar by the CPY of RN033410. Thenormalized CPY of bars without Cr is 48-82% compares to 82-100% for theCr-containing bars

Limiting the Cr level would be desirable due to the abrasiveness ofCr-silicides, which is demonstrated in FIG. 26. FIG. 26A shows wear on atool steel ball which was slid for 3000 linear inches (1500 inches oneach side of the strip) under a 100 gm load over the strip surface withlard oil as a lubricant of a non-Cr sample (RN033407) that was plantsolution annealed at 975° C., cold rolled 25% then aged a 450° C. andsulfuric acid cleaned, while FIG. 26B has a similar condition using asample of a Cr-containing alloy (RN834062). The polished appearance ofthe ball shown in FIG. 26 shows that the Cr-containing alloy caused muchmore wear, leading to a significantly larger volume of material beingremoved from the ball. This is seen in FIG. 26 as a much larger wearscar for the Cr-containing alloy. The larger wear scar suggests thatduring stamping of a sheet of the alloy into parts, a high amount oftool wear would occur.

TABLE 19 Alloys used in Example 9 Alloy Ni Co Cr Si Mg K224 3.71 0.91 01.14 — K225 3.71 0.93 0.11 1.19 0.030 K226 3.61 0.82 0.23 1.20 0.035K227 3.50 0.95 0.34 1.20 0.035 K228 3.51 0.85 0.46 1.21 0.040 K229 3.390.85 0.55 1.20 0.043

TABLE 20 Compositions of plant-cast bars of Example 9¹ Bar Ni Co Cr SiMg RN032037 3.71 0.75 — 1.09 0.12 RN032038 RN033407 3.66 0.88 — 1.070.106 RN033408 RN033409 3.83 0.89 0.45 1.22 0.138 RN033410 RN834059 3.240.758 0.425 1.02 0.094 RN834060 RN834061 3.45 0.74 0.44 1.14 0.076RN834062

TABLE 21 Milling data for plant-cast bars of Example 9 CPY % Bar Type(NORMALIZED) RN032037 Non Cr 75.2% RN032038 Non Cr 48.1% RN033407 Non Cr76.0% RN033408 Non Cr 82.3% RN033409 Cr 95.6% RN033410 Cr  100% RN834059Cr 92.1% RN834060 Cr 90.1% RN834061 Cr 87.7% RN834062 Cr 82.0%

A single casting run produced three bars with the composition shown inTable 21a. Casting plant yield of the bars, which was normalizedsimilarly to the data of Table 21 where RN033410 is considered 100%, isgiven in Table 21b. The CPY of the low-Cr bars compares favorably withthe Cr-containing bars of Table 21. This is believed to be due to Crreducing cracking during hot rolling even at these low levels. RN037969has a normalized CPY % above 100 due to the fact that the yield of thisbar was higher than RN033410 in the earlier example.

TABLE 21a Analyzed compositions of low-Cr bars cast and processed in theplant Bar Ni Co Cr Si Mg 037969 3.70 0.98 0.059 1.07 0.093 037970 037971

TABLE 21b CPY % Bar Type (normalized) RN037969 Low-Cr 102.1%  RN037970Low-Cr 89.8% RN037971 Low-Cr 68.4%

Example 10 Effect of Cr, Mn

A series of ten pound laboratory ingots with the compositions listed inTable 22 were melted in a silica crucible and Durville cast into steelmolds, which after gating were approximately 4″×4″×1.75″. FIG. 27 is aflow chart of the process of this Example 10. Alloy K259 contains asmaller level of Cr than those alloys in Example 9, to investigate thelower limits of the beneficial effect of Cr on hot rolling. Alloys K251,K254 and K260 contain low levels of Mn, to determine if Mn affects hotreliability in the alloy of this invention. The ingots were thenmachined to have tapered edges, as illustrated schematically in FIG. 23,to create a higher state of tensile stress at the edges. The alloys weresoaked for two hours at 900° C., and rolled in two passes to 1.12″(1.4″/1.12″) then water quenched. After examination for cracks, the barswere reheated at 900° C. for two hours, and rolled in three passes to0.50″ (0.9″/0.7″/0.5″), followed by a water quench. K259, with 0.058%Cr, hot rolled without edge crack formation. The Mn-containing alloys,along with K261 (with neither Cr nor Mn) developed large edge cracks.Thus a Cr addition near 0.05%, with a preferred range of 0.025 to 0.1%Cr, appears to be appropriate to balance hot rollability and formationof abrasive particles that would lead to tool wear.

The quenched bars were then soaked at 590° C. for 6 hours, trimmed andthen milled to remove surface oxides developed during hot rolling. Thealloys were then cold rolled to 0.012″ and solution heat treated in afluidized bed furnace for 60 seconds at 950° C. Alloys were thensubjected to an aging anneal of 475° C. for 3 hours, designed toincrease strength and conductivity. The alloys were then cold rolled 25%to 0.009″ and aged at 300° C. for 3 hours. Alternatively, after solutionheat treatment the alloys were cold rolled 25% to 0.009″, given an aginganneal at 475° C. for 3 hours, cold rolled 22% to 0.007″, and given afinal anneal of 300° C. for 3 hours. Properties after the final age forboth process paths are listed in Table 23. For both processes, theexceptionally good property combination of 150 ksi yield strength and atleast 31% IACS are achieved, with low levels of Cr, Mn or neither.Conductivity and yield strength are plotted in FIGS. 28 and 29 againstthe stoichiometric ratio ((Ni+Co)/(Si−Cr/5)) along with data fromexample 8 to demonstrate the unusually good properties reached when theratio is kept between 3.0 and 5.0.

TABLE 22 Low Cr and Mn alloys of Example 10 Alloy Ni Co Si Mg Cr MnRatio* K251 3.64 0.84 1.16 0.058 — 0.026 3.862 K254 3.73 0.90 1.16 0.044— 0.061 3.991 K259 3.78 0.56 1.14 0.073 0.058 0.004 3.846 K260 3.75 0.941.15 0.065 <.001 0.048 4.078 K261 3.79 0.95 1.16 0.054 <.001 0.004 4.086*Ratio = (Ni + Co)/(Si − Cr/5)

TABLE 23 Properties for Example 10 SA-age-CR-age processSA-CR-age-CR-age process % 90° % 90° Alloy IACS YS/TS/EI MBR/t IACSYS/TS/EI MBR/t K251 31.0 149.9/156.5/1 4.0/5.2 32.0 151.9/158.6/32.6/2.9 K254 33.7 141.2/144.7/2 3.3/3.3 33.0 151.7/158.1/1 2.3/3.7 K25931.8 151.0/157.3/2 4.0/5.2 33.3 150.8/156.9/2 2.3/2.9 K260 32.4149.9/156.3/3 3.8/3.8 35.3 148.6/154.7/3 2.9/4.3 K261 31.9 150.9/157.1/23.8/5.2 34.4 151.0/157.6/2 2.6/4.3

Example 11 Effect of Processing

Sections of plant cast bar RN032037, whose composition is in Table 20,were processed from plant hot rolled and coil milled plate 0.600″ thick.Samples were further processed by a variety of processing paths shown inFIG. 30. Process A involved cold rolling to 0.012″ and solution heattreating in a fluidized bed furnace for 60 seconds at 950° C., ageannealing at 500° C. for 3 hours, cold rolling 25% to 0.009″, and givinga second anneal at 350° C. for 4 hours. In process B, the metal wasrolled to 0.050″ and given an intermediate bell anneal (“IMBA”) of 575°C. for 8 hours. Then the samples were subject to cold rolling to 0.012″and solution heat treating in a fluidized bed furnace for 60 seconds at950° C., age annealing at 500° C. for 3 hours, cold rolling 25% to0.009″, and giving a second anneal at 350° C. for 4 hours, In process C,The alloy was rolled to 0.024″ and solution heat treated in a fluidizedbed furnace for 60 seconds at 950° C., followed by cold rolling to0.012″ and a second solution heat treatment in a fluidized bed furnacefor 60 seconds at 950° C. Subsequently, the process involved ageannealing at 500° C. for 3 hours, cold rolling 25% to 0.009″, and givinga second anneal at 350° C. for 4 hours. In process D, cold rolling to0.012″ was followed by solution heat treatment in a fluidized bedfurnace for 60 seconds at 950° C. the alloy was cold rolled 25% to0.009″, given an aging anneal at 475° C. for 3 hours, cold rolled 22% to0.007″, and given a final anneal of 300° C. for 3 hours. In process E,the metal was rolled to 0.050″ and given an intermediate bell anneal of575° C. for 8 hours. Then the samples were rolled to 0.024″ and solutionheat treated in a fluidized bed furnace for 60 seconds at 950° C.,followed by cold rolling to 0.012″ and a second solution heat treatmentin a fluidized bed furnace for 60 seconds at 950° C. Subsequently, theprocess involved age annealing at 500° C. for 3 hours, cold rolling 25%to 0.009″, and giving a second anneal at 350° C. for 4 hours.

TABLE 24 Properties resulting from the processes of Example 11 ProcessDescription YS/TS/EI % IACS 90° MBR/t A “Standard” process 145.1/152.7/336.2 4.0/7.0 B IMBA process 144.4/150.4/3 37.4 3.8/4.0 C Double solutionanneal 147.2/152.7/3 37.1 3.6/6.9 process D SA-CR-age-CR-age146.5/154.4/2 34.2 4.2/8.7 process E IMBA-double SA 143.6/150.1/3 36.73.3/7.0 process

Example 12 Effect of Processing

Sections of plant cast bar RN032037, whose composition is in Table 20,were processed from plant hot rolled and coil milled plate 0.600″ thick.Process variables were systematically varied to explore a matrixcontaining ranges of processing conditions. FIG. 31 is a flow chart ofthe process of this Example 12. After cold rolling to 0.012″, sampleswere solution annealed in a fluidized bed furnace at temperatures of925, 950, 975 and 1000° C. for 60 seconds. Coupons were then given ageanneals at temperatures of 450, 475, 500 and 525° C. for three hours.Samples were then cold rolled to final thickness at varying reductionsof 15, 25 and 35%. Finally, samples were given a second age anneal forfour hours at 300, 325, 350 and 375° C. Table 25 contains properties ofsamples with different solution anneal temperatures while the rest ofthe process was held constant. As solution temperature is increased,yield strength increases, while conductivity decreases. Additionally,bend formability worsens at the higher solution annealing temperatures,due to the large grain size developed during the 975 and 1000° C.anneals. Thus a solution annealed grain size below 20 μm is preferred.

When the temperature of the first age is varied while the otherprocessing variables are held constant, it is found that the higheststrength levels are due to the intermediate aging temperatures, as shownfor the 475 and 500° C. ages in Table 26. Also, the conductivityincreased with increasing aging temperature. Thus the first agetemperature can be manipulated to provide various desirable combinationsof strength and conductivity.

When the roll reduction between the first and second ages was varied,yield strength was found to increase with increasing reduction, in thiscase up to 35%, while conductivity was unaffected. A larger increase instrength was found when going from 15 to 25% reduction than when goingfrom 25 to 35%. Bend formability was found to worsen with higherreductions. The roll reduction can be manipulated to affect thestrength-formability characteristics of the material produced. Use ofroll reduction above 35% may be useful to produce peak strength, albeitwith poorer formability.

Table 28 shows that the second age anneal temperature does not have alarge effect on properties when the other processing variables are heldconstant. Conductivity was found to increase as the temperature of thesecond age increased, but to a small degree. Thus a wide operating rangeis acceptable for this step of the process.

TABLE 25 Effect of varying solution anneal temperatures, with 475° C.first age, 25% roll reduction, 350° C. second age of Example 12 SAtemperature, SA grain size, ° C. μm YS/TS/EI % IACS 90° Bends 925 9.0142.3/147.7/3 36.0 6.0/6.0 950 12.9 145.9/152.3/3 34.1 6.1/6.1 975 26.1146.5/152.6/2 32.3  6.1/12.1 1000 28.8 147.5/152.1/3 32.7  8.7/12.1

TABLE 26 Effect of varying first age temperatures, with 950° C. solutionanneal, 25% roll reduction, 350° C. second age of Example 12 1^(st) AgeTemp, ° C. YS/TS/EI % IACS 90° Bends 450 140.1/145.2/4 30.5 4.0/6.1 475145.9/152.3/3 34.1 6.1/6.1 500 145.1/152.7/3 36.2 4.0/7.0 525133.2/134.5/1 39.9 n/m* *not measured

TABLE 27 Effect of varying roll reductions, with 950° C. solutionanneal, 475° C. first age, 350° C. second age Roll reduction YS/TS/EI %IACS 90° Bends 15% 138.4/145.0/4 33.9 5.4/5.4 25% 145.9/152.3/3 34.16.1/6.1 35% 148.9/155.5/3 34.0  7.1/10.0

TABLE 28 Effect of varying second age temperatures, with 950° C.solution anneal, 475° C. first age, 25% roll reduction 2^(nd) Age Temp,° C. YS/TS/EI % IACS 90° Bends 300 146.4/152.0/2 33.2 6.1/6.1 325146.5/152.3/3 33.6 6.1/8.7 350 145.9/152.3/3 34.1 6.1/6.1 375146.2/152.7/3 34.8 6.0/8.6

Samples from the Cr-free plant-cast bar RN033407 (composition in Table20) were rolled in the laboratory from the coil milled condition at0.460″ down to 0.012″. Subsequently samples were solution heat treatedin a fluidized bed furnace for 60 seconds at 900° C. Coupons were thenrolled 25% to 0.009″ and age annealed at 425, 450 and 475° C. for timesof 4 and 8 hours at each temperature. Subsequently samples were coldrolled 22% to 0.007″ and given a final anneal of 300° C. for threehours. The best combination of strength and conductivity resulted fromthe 450° C. for 8 hour age, with the properties from that condition andothers listed in Table 28a. Comparing the 450° C./8 hr data to theproperties in Table 25, it is clear that further reducing the solutionannealing temperature to 900° C. lowers the yield strength and increasesconductivity to produce the unique combination of 140 ksi and 39% IACS.In addition, the processing including a 900° C. solution annealingtemperature produced improved bend formability when compared toprocessing involving higher solution anneal temperatures.

TABLE 28A Properties after processing which includes a 900° C. solutionanneal. 1^(st) age condition SA grain size, μm YS/TS/EI % IACS 90° Bends450° C./4 hr 5.5 138.5/143.0/2 36.1 2.6/4.0 450° C./8 hr 5.5140.3/144.7/2 39.0 2.0/4.3 475° C./4 hr 5.5 126.9/131.7/3 40.7 2.3/4.0475° C./8 hr 5.5 131.0/135.0/3 41.2 1.7/2.3

Example 13 Effect of Si and Mg

Laboratory ingots with the compositions listed in Table 29 were meltedin a graphite crucible and Tamman cast into steel molds, which aftergating were 4.33″×2.17″×1.02″. All alloys were targeted to have aCr-content of 0.5%. The Si-content was varied between 1.0% and 1.5%. Forthe high-Si 1.5% variants the Ni/Co ratio was varied between 4.98 and11.37 with a fixed stoichiometric ratio ((Ni+Co)/(Si−Cr/5)) around 4.The influence of Mg was tested by alloy BW with the same alloycomposition as BV but with additionally 0.1% Mg.

FIG. 32 is a flow chart of the process of this Example 13. After soakingtwo hours at 900° C. they were hot rolled to 0.472″, thereby reheatedafter each pass at 900° C. for 10 minutes. After the last pass the barwas water quenched. After trimming and milling to 0.394″ in order toremove the surface oxide, the alloys were cold rolled to 0.012″ andsolution heat treated in a fluidized bed furnace for the time andtemperature listed in Table 29. Time and temperature were selected toachieve grain sizes below 20 μm.

Subsequently the alloys were cold rolled 25% to 0.009″ then subjected toan aging anneal of 450 and 475° C. for 3 hours. Properties of samplesare listed in Table 30. The formability was measured via V-block. Withincreasing Si-content the yield strength is increasing from 121 ksi forthe 1.05% Si alloy to 135 ksi for the 1.51% Si alloy. For the 1.16% Sivariants Mg results in a benefit to yield strength of 5-7 ksi. Loweringthe Ni/Co ratio from 11.37 to 4.98 enhances yield strength for the highSi (1.5%) alloys. Stress relaxation was tested by the ring method with atarget initial stress of 0.8 times yield strength. Table 31 shows thestress relaxation data for variants BV, BW and BX. Comparing BV and BW,due to Mg addition the stress relaxation resistance increases from 66.3%to 86.6% for the 150° C./1000 h condition and from 48.5% to 72.3% forthe 200° C./1000 h condition. The stress relaxation resistance of thehigher Si-containing BX amounts to 82.3% for the 150° C./1000 hcondition and 68.7% for the 200° C./1000 h condition.

TABLE 29 Alloys of Examples 13 and 15, wt % alloy Ni Co Cr Si Mg Ratio*Ni/Co SA conditions Grain size, μm BU 3.08 0.69 0.57 1.05 4.03 4.46 950°C. - 1 minute 10-15 BV 3.51 0.75 0.49 1.16 4.01 4.68 950° C. - 1 minute10-15 BW 3.52 0.78 0.51 1.16 0.11 4.06 4.51 950° C. - 1 minute 15 BT4.04 1.15 0.47 1.41 3.94 3.51 975° C. - 1 minute  5 BX 4.89 0.43 0.501.48 3.86 11.37 975° C. - 1 minute 15-20 BY 4.48 0.90 0.51 1.51 3.824.98 975° C. - 1 minute 10 *Ratio = (Ni + Co)/(Si − Cr/5)

TABLE 30 Properties fro SA-Cr-AA Process of Example 13 Alloy AA T, ° C.YS, ksi % IACS 90° MINBR/t BU 450 121.0 27.6 2.2/1.3 BV 450 121.8 32.51.7/1.3 475 120.5 34.8 n.m. BW 450 126.9 31.8 2.2/2.6 475 127.6 34.4n.m. BT 450 127.5 28.6 n.m. 475 128.9 32.1 n.m. BX 450 129.5 29.12.6/2.6 475 125.9 31.1 n.m. BY 450 135.2 30 2.2/2.2 475 134.0 31.43.4/2.1

TABLE 31 Stree Relaxation of Process SA-CR 25%-AA 450° C./3 h of Example13 remaining stress (%) Alloy YS, ksi % IACS 150° C./1000 h 200° C./1000h BV 121.8 32.5 66.3 48.5 BW 126.9 31.8 86.6 72.3 BX 129.5 29.1 82.368.7

Example 14 Effect of Si and Mg

FIG. 33 is a flow chart of the process of this Example 14. Specimens ofExample 13 were subsequently cold rolled to 0.007″ with a cold reductionof 22%. Thereafter the samples were aged annealed at temperatures of300° C. to 400° C. for 3 hours. Properties from samples given secondages at 300° C. are listed in Table 32. The formability was measured viaV-block.

The highest yield strength was achieved with a first aging temperatureof 450° C. With increasing Si-content the yield strength is increasingfrom 131 ksi for the Si 1.05% alloy to 147 ksi for the Si 1.51% alloy.For the Si 1.16% variants Mg results in a benefit to yield strength of7-10 ksi. Lowering the Ni/Co ratio from 11.37 to 4.98 enhances yieldstrength for the high Si 1.5% alloys by 3 ksi. Stress relaxation wastested by the ring method with a target initial stress of 0.8 timesyield strength. Table 33 shows the stress relaxation data for BV, BW andBX for the process SA-CR -1.AA 450° C.-CR -2.AA 300° C.

Comparing BV and BW, due to Mg addition the stress relaxation resistanceincreases from 72.6% to 85.6% for the 150° C./1000 h condition and from55.8% to 69.3% for the 200° C./1000 h condition. The stress relaxationresistance of the higher Si-containing BX amounts to 81.1% for the 150°C./1000 h condition and 66.1% for the 200° C./1000 h condition.

TABLE 32 Properties from SA-CR-1AA-CR-2AA Process of Example 14 2.AA300° C./3 h YS, Alloy 1.AA T, ° C. ksi TS, ksi A10, % % IACS 90° MINBR/tBU 450 130.7 138.1 2.6 33.6 5.5/5.5 BV 450 137.4 144.5 3.7 31.4 2.8/5.6475 130.8 137.8 4.8 34.8 2.8/5.0 BW 450 144.0 143.6 2.3 32.1 3.3/7.8 475141.3 147.1 3.8 34 2.8/6.7 BT 450 144.6 152.4 2.9 29.8 4.0/8.0 475 137.8146.2 4.2 34.1 4.0/7.0 BX 450 143.7 155.2 2.8 28.6 3.3/7.8 475 134.4148.2 2.8 31.2 2.8/6.7 BY 450 146.6 155.8 3 29.6 3.3/6.7 475 137.8 150.04.3 32.2 3.3/6.7

TABLE 33 Stress Relaxation Process SA-CR-1AA450° C.-CR-2AA300° C. ofExample 14 remaining stress (%) Alloy YS, ksi % IACS 150° C./1000 h 200°C./1000 h BV 137.4 31.4 72.6 55.8 BW 144.0 32.1 85.6 69.3 BX 143.7 28.681.1 66.1

Example 15 Effect of Si and Mg

Laboratory ingots with the compositions listed in Table 34 were meltedin a graphite crucible and Tamman cast into steel molds, which aftergating were 4.33″×2.17″×1.02″. The alloys were Cr-free and with astoichiometric ratio ((Ni+Co)/(Si−Cr/5)) around 4.2. The Ni/Co ratio wasabout 4.5. Two alloys have a targeted Si-content of 1.1%, but varyingMg-content and one alloy has an Si-content of 1.4% and additionally Mg.FIG. 34 is a flow chart of the process of this Example 15. After soakingtwo hours at 900° C. they were hot rolled to 0.472″, thereby reheatedafter each pass at 900° C. for 10 minutes. After the last pass the barwas water quenched. After trimming and milling to 0.394″ in order toremove the surface oxide, the alloys were cold rolled to 0.012″ andsolution heat treated in a fluidized bed furnace for the time andtemperature listed in Table 34. Time and temperature were selected toachieve grain sizes below 20 μm.

Subsequently the alloys were cold rolled 25% to 0.009″ then subjected toan aging anneal of 450 and 475° C. for 3 hours. Properties of samplesare listed in Table 35. The yield strength, formability measured withV-block and conductivity of the Cr-free FL and FM are similar to theCr-containing BV and BW from Example 13, with comparable Si-content of1.1%, Ni/Co ratio and stoichiometric ratio. As in Example 13, anaddition of 0.1% Mg results in a benefit to yield strength of 7-8 ksi.

With increasing Si-content from 1.17% to 1.39% the yield strength isincreasing from 126.6 to 130.5 ksi at the same solution annealingtemperature. For variant FN, increasing the solution annealingtemperature from 950° C. to 1000° C. results in an increase of yieldstrength of 10 ksi.

Stress relaxation was tested by the ring method with a target initialstress of 0.8 times yield strength. Table 36 shows the stress relaxationdata for the processes with a solution annealing temperature of 950° C.Compared to the Cr-containing 1.16% Si samples of Example 13, BV and BW,the stress relaxation of FL and FM is slightly lower. Similar to Example13, a Mg addition of 0.1% results in a stress relaxation increase from64.6% to 82.7% for the 150° C./1000 h condition and from 44.3% to 69.2%for the 200° C./1000 h condition. The stress relaxation resistance ofthe Mg-containing, Si 1.39% variant FN amounts to 84.1% for the 150°C./1000 h condition and 65.9% for the 200° C./1000 h condition.

TABLE 34 Alloys at Examples 15 and 16, wt. % alloy Ni Co Cr Si Mg Ratio*Ni/Co SA conditions Grain size, μm FL 3.71 0.90 1.09 4.23 4.12  950°C. - 1 minute 10 FM 3.89 0.87 1.17 0.10 4.05 4.47  950° C. - 1 minute 5-10 FN 5.19 0.99 1.39 0.10 4.47 4.90  950° C. - 1 minute 10 1000° C. -1 minute 15-20 *Ratio = (Ni + Co)/(Si − Cr/5)

TABLE 35 Properties from SA-CR-AA Process of Example 15 AA T, 90°MINBR/t Alloy SA-conditions ° C. YS, ksi % IACS GW/BW FL  950° C. - 1minute 450 118.6 29.5 2.6/1.3 475 119.4 34.5 3.0/1.7 FM  950° C. - 1minute 450 126.6 30.2 2.6/2.2 475 126 33.1 2.1/2.1 FN  950° C. - 1minute 450 130.5 30.7 3.0/2.6 475 129.1 33.1 2.6/2.2 1000° C. - 1 minute450 141.7 27.1 3.5/3.9 475 139.2 29.6 3.5/4.8

TABLE 36 Stress Relaxation of Process SA 950° C.-CR 25%- AA 450° C./3 hof Example 15 remaining stress (%) Alloy YS, ksi % IACS 150° C./1000 h200° C./1000 h FL 118.6 29.5 64.6 44.3 FM 126.6 30.2 82.7 69.2 FN 130.530.7 84.1 65.9

Example 16 Effect of Si and Mg

FIG. 35 is a flow chart of the process of this Example 16. Specimens ofExample 15 were subsequently cold rolled to 0.007″ with a cold reductionof 22%. Thereafter the samples were aged annealed at temperatures of300° C. to 350° C. for 3 hours. Properties from samples given secondages at 300° C. are listed in Table 37. The formability was measured viaV-block. The highest yield strength was achieved with a first agingtemperature of 450° C.

FM shows a higher yield strength of 11 ksi in comparison to FL, that ispartly ascribed to the Mg-content and partly ascribed to the slightlyhigher Si-content. The yield strength, bendability and conductivity ofthe Cr-free FL and FM are similar to the Cr-containing BV and BW fromexample 15, with comparable Si-content, Ni/Co ratio and stoichiometricratio.

Increasing Si-content from 1.17% to 1.39% leads to the same yieldstrength of about 144 ksi for a solution annealing temperature of 950°C. For variant FN, increasing the solution annealing temperature from950° C. to 1000° C. results in an increase of yield strength from 143 to158 ksi.

Stress relaxation was tested by the ring method with a target initialstress of 0.8 times yield strength. Table 38 shows the stress relaxationdata for FL and FM for the process SA 950° C.-CR-1.AA 450° C.-CR -2.AA300° C. Compared to the Cr-containing 1.16% Si samples of example 15, BVand BW, the stress relaxation of FL and FM is lower by 2-3%. Similar toexample 15, a Mg addition of 0.1% results in a stress relaxationincrease from 70.0% to 82.0% for the 150° C./1000 h condition and from52.3% to 66.9% for the 200° C./1000 h condition. The stress relaxationresistance of the Mg-containing, Si 1.39% variant FN amounts to 85.0%for the 150° C./1000 h condition and 66.4% for the 200° C./1000 hcondition.

TABLE 37 Properties from SA-CR-1AA-CR-2AA Process of Example 16 2.AA300° C./3 h Alloy SA-conditions 1.AA T, ° C. YS, ksi TS, ksi A10, % %IACS 90° MINBR/t GW/BW FL  950° C. - 1 minute 450 133.1 140 2.7 31.64.5/6.1 475 129.7 139.5 1.9 36.2 3.9/4.4 FM  950° C. - 1 minute 450 144147.6 2 31 4.4/7.2 475 141.3 145 1.8 33.2 4.5/6.8 FN  950° C. - 1 minute450 143.2 150.0 2 31.5 3.9/7.2 475 133.1 138.9 2.4 34.3 3.3/5.6 1000°C. - 1 minute 450 158.1 165.1 1.4 27.6 5.0/9.4 475 157.5 164.6 1.9 30.94.4/8.3

TABLE 38 Stress Relaxation of Process SA 950° C.-CR-1AA 450° C.-CR-2AA300° C. of remaining stress (%) Alloy YS, ksi % IACS 150° C./1000 h 200°C./1000 h FL 133.1 31.6 70.1 52.3 FM 144.0 31 82.0 66.9 FN 143.2 31.685.0 66.4

Example 16

FIG. 36 shows the relation between 90°-minBR/t BW and yield strength forthe alloys and processes of Examples 13, 14, 15, and 16. Both processesSA-CR-AA and SA-CR-AA-CR-AA form two groups with a certainformability-yield strength relation. The solid lines are just a guide tothe eye and mark increasing Min BR/t and increasing yield strength withhigher Si-content and/or Mg-addition. There is almost no difference inyield strength and formability-yield strength relationship between theCr-containing and Cr-free variants.

FIG. 37 shows the relation between % IACS and yield strength for thealloys and processes of Examples 13, 14, 15, and 16. The Cr-free and theCr-containing alloys show the same capability in achieving aconductivity of 30% IACS together with high yield strength. TheSA-CR-AA-CR-AA process achieves higher yield strength than the SA-CR-AAprocess, but at the same conductivity.

1. A copper base alloy having an improved combination of yield strengthand electrical conductivity consisting essentially of: between about 1.0and about 6.0 weight percent Ni; up to about 3.0 weight percent Co;between about 0.5 and about 2.0 weight percent Si; between about 0.01and about 0.5 weight percent Mg; up to about 1.0 weight percent Cr; upto about 1.0 weight percent Sn, and up to about 1.0 weight percent Mn,the balance being copper and impurities, the alloy processed to have ayield strength of at least about 137 ksi, and an electrical conductivityof at least about 25% IACS.
 2. The alloy according to claim 1 whereinthe alloy has a conductivity of at least about 30% IACS.
 3. The alloyaccording to claim 1 wherein the alloy is processed to have a yieldstrength of at least about 137 ksi, and an electrical conductivity of atleast about 38% IACS.
 4. The alloy according to claim 1 wherein thealloy is processed to have a yield strength of at least about 143 ksi ,and an electrical conductivity of at least about 37% IACS.
 5. The alloyaccording to claim 1 wherein the alloy is processed to have a yieldstrength of at least about 157 ksi, and an electrical conductivity of atleast about 32% IACS.
 6. A copper base alloy having an improvedcombination of yield strength and formability consisting essentially of:between about 1.0 and about 6.0 weight percent Ni; up to about 3.0weight percent Co; between about 0.5 and about 2.0 weight percent Si;between about 0.01 and about 0.5 weight percent Mg; up to about 1.0weight percent Cr; up to about 1.0 weight percent Sn, and up to about1.0 weight percent Mn, the balance being copper and impurities, thealloy processed to have a yield strength of at least about 137 ksi, andan mbr/t of less than 4 t for both good way bends and bad way bends. 7.The copper base alloy according to claim 6 wherein the alloy has anmbr/t of less than about 2 t for both good way bends and bad way bends.8. The copper base alloy according to claim 6 wherein the alloy has anelectrical conductivity of at least about 25% IACS.
 9. The copper basealloy according to claim 8 wherein the alloy has an electricalconductivity of at least about 30% IACS.
 10. A copper base alloy havingan improved combination of yield strength, electrical conductivity, andformability, consisting essentially of: between about 1.0 and about 6.0weight percent Ni; up to about 3.0 weight percent Co; between about 0.5and about 2.0 weight percent Si; between about 0.01 and about 0.5 weightpercent Mg; up to about 1.0 weight percent Cr; up to about 1.0 weightpercent Sn, and up to about 1.0 weight percent Mn, the balance beingcopper and impurities, the ratio of (Ni+Co)/(Si−Cr/5) being betweenabout 3 and about
 7. 11. The alloy according to claim 10 wherein thealloy is processed to have an mbr/t of less than about 4 t for both goodway bends and bad way bends.
 12. The alloy according to claim 10 whereinthe alloy is processed to have an mbr/t of less than about 2 t for bothgood way bends and bad way bends.
 13. The alloy according to claim 10wherein the alloy is processed to have a yield strength of at leastabout 137 ksi, and an electrical conductivity of at least about 38%IACS.
 14. The alloy according to claim 10 wherein the alloy is processedto have a yield strength of at least about 143 ksi , and an electricalconductivity of at least about 37% IACS.
 15. The alloy according toclaim 10 wherein the alloy is processed to have a yield strength of atleast about 157 ksi, and an electrical conductivity of at least about32% IACS.
 16. The cooper base alloy according to claim 1 wherein thealloy is in the form of foil, wire, bar or tube.
 17. A copper base alloyhaving an improved combination of yield strength, electricalconductivity, and formability, consisting essentially of: between about3.0 and about 5.0 weight percent Ni; up to about 2.0 weight percent Co;between about 0.7 and about 1.5 weight percent Si; between about 0.03and about 0.25 weight percent Mg; up to about 0.6 weight percent Cr; upto about 1.0 weight percent Sn, and up to about 1.0 weight percent Mn,the balance being copper and impurities, the ratio of (Ni+Co)/(Si−Cr/5)being between about 3 and about
 7. 18. A copper base alloy having animproved combination of yield strength, electrical conductivity, andformability, consisting essentially of: between about 3.0 and about 5.0weight percent Ni; up to about 2.0 weight percent Co; between about 0.7and about 1.5 weight percent Si; between about 0.03 and about 0.25weight percent Mg; up to about 0.6 weight percent Cr; up to about 1.0weight percent Sn, and up to about 1.0 weight percent Mn, the balancebeing copper and impurities, the alloy processed to have a yieldstrength of at least about 137 ksi, and an electrical conductivity of atleast about 25% IACS.
 19. The alloy according to claim 18 wherein thealloy is processed to have a yield strength of at least about 137 ksi,and an electrical conductivity of at least about 38% IACS.
 20. The alloyaccording to claim 18 wherein the alloy is processed to have a yieldstrength of at least about 143 ksi, and an electrical conductivity of atleast about 37% IACS.
 21. The alloy according to claim 18 wherein thealloy is processed to have a yield strength of at least about 157 ksi,and an electrical conductivity of at least about 32% IACS.
 22. A copperbase alloy having an improved combination of yield strength, electricalconductivity, stress relaxation resistance, consisting essentially of:between about 3.5 and about 3.9 weight percent Ni; between about 0.8 andabout 1.0 weight percent Co; between about 1.0 and about 1.2 weightpercent Si; between about 0.05 and about 0.15 weight percent Mg; up toabout 0.1 weight percent Cr; up to about 1.0 weight percent Sn, and upto about 1.0 weight percent Mn, the balance being copper and impurities,the alloy processed to have a yield strength of at least about 140 ksi,and an electrical conductivity of at least about 30% IACS.
 23. The alloyaccording to claim 22 wherein the ratio of (Ni+Co)/(Si−Cr/5) is betweenabout 3.5 and about 5.0.
 24. The alloy according to claim 23 wherein theration of Ni/Co is between about 3 and about
 5. 25. The alloy accordingto claim 22 wherein the ration of Ni/Co is between about 3 and about 5.26. A process for making a copper base alloy including nickel, silicon,cobalt and chromium, comprising: melting and casting the alloy; hotrolling from about 750° to about 1050° C.; cold rolling to a convenientgauge for solutionizing; solution annealing the alloy at between about800° and about 1050° C. for from about 10 seconds to about one hour; andsubsequently quenching or rapidly cooling the alloy to ambienttemperature to obtain an electrical conductivity of less than about 20%IACS (11.6 MS/m) and an equiaxed grain size of about 5-20 μm; coldrolling the alloy for a 0 to about 75% reduction in thickness;subjecting the alloy to an hardening anneal at about 300° to about 600°C. for about 10 minutes to about 10 hours; subsequently cold rolling thealloy for an about 10 to about 75% reduction in thickness to finishgauge; subjecting the alloy to a second age hardening anneal at 250 toabout 500° C. for about 10 minutes to about 10 hours to achieve.
 27. Theprocess according to claim 26 further comprising an intermediaterecrystallization anneal after the hot rolling.
 28. The processaccording to claim 26 wherein the alloy consists essentially of betweenabout 1.0 and about 6.0 weight percent Ni; up to about 3.0 weightpercent Co; between about 0.5 and about 2.0 weight percent Si; betweenabout 0.01 and about 0.5 weight percent Mg; up to about 1.0 weightpercent Cr; up to about 1.0 weight percent Sn, and up to about 1.0weight percent Mn, the balance being copper and impurities.
 29. Theprocess according to claim 28 wherein the alloy consists essentially of:between about 3.0 and about 5.0 weight percent Ni; up to about 2.0weight percent Co; between about 0.7 and about 1.5 weight percent Si;between about 0.03 and about 0.25 weight percent Mg; up to about 0.6weight percent Cr; up to about 1.0 weight percent Sn, and up to about1.0 weight percent Mn, the balance being copper and unavoidableimpurities.
 30. The process according to claim 29 wherein the ratio of(Ni+Co)/(Si−Cr/5) being between about 3 and about
 7. 31. The processaccording to claim 29 wherein the alloy comprises between about 3.5 andabout 3.9 weight percent Ni; between about 0.8 and about 1.0 weightpercent Co; between about 1.0 and about 1.2 weight percent Si; betweenabout 0.05 and about 0.15 weight percent Mg; up to about 0.1 weightpercent Cr; up to about 1.0 weight percent Sn, and up to about 1.0weight percent Mn, the balance being copper and impurities.